Power dispatch system for electrolytic production of hydrogen from wind power

ABSTRACT

A system for distributing medium voltage DC electric power from a wind farm to electrolyser modules requiring low voltage DC power. The system includes one or more of each of central step down DC-DC converters, DC buses, regulated DC-DC converters, respective electrolyser module controllers, dispatch controllers, alternative loads, and alternative power sources.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. application Ser. No. 12/606,517filed Oct. 27, 2009, which claims the benefit and priority of U.S.Provisional No. 61/193,124 filed Oct. 30, 2008. The entire disclosuresof the above applications are incorporated herein by reference in theirentireties.

FIELD OF THE INVENTION

The present invention relates to the distribution of wind generatedelectricity to electrolyser modules for the production of hydrogen gas.

BACKGROUND OF THE INVENTION

Hydrogen is an important industrial gas, widely used in oil refining,and production of synthetic fuels, ammonia, and methanol. Hydrogen alsois being considered for future use in hydrogen vehicles powered byhydrogen fuel cell engines or hydrogen internal combustion engines (orhybrid hydrogen vehicles, also partially powered by batteries). Most ofthe current supply of hydrogen is produced by steam methane reforming,using natural gas feedstock. With finite supplies of fossil-based energyresources such as natural gas and increasing prices of these energyresources, as well as the possibility of the imposition of carbonemission taxes, the cost, and eventually the availability, of hydrogenwill be adversely affected unless an alternative clean and sustainable“feedstock” can be implemented.

Wind resources represent a potential source of large amounts ofsustainable and clean energy. With recent increases in the cost ofnatural gas, the concept of using wind turbine generators in “windfarms” to supply sustainable, clean and relatively low cost electricalpower to electrolysers for large scale production of “green” hydrogen isbecoming an economically viable approach.

Electrolysers use DC electricity to transform reactant chemicals todesired product chemicals through electrochemical reactions, i.e.,reactions that occur at electrodes that are in contact with anelectrolyte. Electrolysers that can produce hydrogen include: waterelectrolysers, which produce hydrogen and oxygen from water andelectricity; ammonia electrolysers, which produce hydrogen and nitrogenfrom ammonia and electricity; and, chlor-alkali electrolysers, whichproduce hydrogen, chlorine and caustic solution from brine andelectricity.

Water electrolysers are the most common type of electrolyser used toproduce gaseous hydrogen. Oxygen also is an important industrial gas,and the oxygen generated may be a saleable product. The most common typeof commercial water electrolyser currently is the alkaline waterelectrolyser. Other types of water electrolysers include PEM waterelectrolysers, currently limited to relatively small productioncapacities, and solid oxide water electrolysers, which have not beencommercialized. Alkaline water electrolysers utilize an alkalineelectrolyte in contact with appropriately catalyzed electrodes. Hydrogenis produced at the surfaces of the cathodes (negative electrodes), andoxygen is produced at the surfaces of the anodes (positive electrodes)upon passage of current between the electrodes. The rates of productionof hydrogen and oxygen are proportional to the DC current flow in theabsence of parasitic reactions and stray currents, and for a givenphysical size of electrolyser.

Wind farms consist of a number of wind turbine generators, generallyspread over a significant geographical area. Wind farms typicallygenerate AC electricity for delivery to an AC utility grid, althoughgeneration of DC power also is possible. AC electricity can easily betransformed to higher voltages for efficient transmission of high powerover long distances. Wind farm total output can range from tens of MW tohundreds of MW. The electrolyser module size could range from below 1 MWup to 5 MW. Dedicated hydrogen generation using electrolyser modules asloads connected to a large wind farm will therefore employ a significantnumber of electrolyser modules.

Large scale, low cost production of “wind hydrogen” (hydrogen producedby water electrolysis using wind power) requires capture of a highpercentage of the wind power generated, the output of which is variableover time. This requirement necessitates firstly the use of multiplelarge scale, low cost water electrolyser modules that can act as highlyvariable loads to cover a wide range of operating power, from low tovery high power densities. An appropriate water electrolyser moduledesign is disclosed in the co-pending application which is incorporatedby reference herein in its entirety. Other necessary elements are anefficient, low cost, and flexible electrical power dispatch system andoperating method to distribute the wind power to the multiple waterelectrolyser modules, as well as effective control of the electrolysermodules to ensure load matching to the wind farm output. An appropriateelectrical power dispatch system and operating and control methods aredescribed herein. Although the description of the invention hereinrelates to “wind hydrogen”, it is to be understood that the inventionalso is applicable to electrolytic production of other chemicals, forexample, direct production of “wind ammonia” using the electrolyserdescribed in US 2008/0193360.

PRIOR ART

Commercial electrolyser systems for industrial applications currentlytypically utilize power supplies, for example, SCR rectifiers, whichconvert AC electricity to regulated DC electricity of the desired powerlevel and current-voltage. However, the best efficiency and power factorof SCR rectifiers is at the nominal power rating; both the efficiencyand power factor drop significantly as the power level is turned down,as is frequently the case for wind powered electrolyser systems. Sinceall of the power fed to the electrolyser modules must pass through thepower dispatch system, the potential effects of SCR rectifierinefficiency are substantial. Furthermore, harmonics levels typicallymay not meet IEEE 519 guidelines, although they are improved through theuse of 12 pulse configurations; this is of concern for large systems.The use of SCR rectifiers also necessitates two transformer stages tostep down the voltage from high voltage AC transmission lines.

Pritchard (U.S. Pat. No. 5,592,028) describes an alternative electricalpower regulation apparatus for a wind hydrogen system that targetsoperation of water electrolyser modules at cell voltages of about 1.6 V,by using switches to vary the number of cells engaged in each of theelectrolyser modules. This apparatus focuses on achieving highelectrolyser module operating voltage efficiency. The correspondingoperating current density will necessarily be low for any given cellconfiguration and set of components. Consequently, in order to capture ahigh percentage of wind power generated by a wind farm, the numberand/or physical size of electrolyser modules will be inordinately large,and the associated capital cost will be relatively high. Notably, a keyfactor for low cost production of wind hydrogen is availability of lowcost wind power (i.e., high wind capacity factors); this, combined withthe significant thermodynamic (i.e., minimum) voltage requirement forwater electrolysis, limits potential cost benefits associated withtargeting high electrolyser module operating efficiency. Pritchard doesnot provide any details of the rest of the corresponding power dispatchsystem or its control, other than the use of an AC-DC converter/filterupstream of the switch apparatus.

Morse (US 2008/0047502) also briefly describes a similar electricalpower conversion apparatus as part of a wind hydrogen system. The unitload can be varied to assure maximum electrolyser module efficiency, forexample, by adjusting the number of active cells. Morse also teachesthat in general AC electricity generated at a wind farm may be steppedup to high voltage and transmitted to a point of use, then stepped downand converted to DC electricity by a full bridge rectifier orequivalent, but provides no further details in this regard.

Doland (US 2008/0127646) describes a system that simultaneously controlsand adjusts both the electrical power output from a wind farm andelectrical power conversion to the requirements of the electrolysermodules. Doland generally mentions functional requirements such asmaximizing the hydrogen produced and minimizing energy losses, but doesnot describe details of how these requirements are to be achieved.

SUMMARY OF THE INVENTION

A system for distributing electric power from a wind farm generatingmedium to high voltage AC electricity to multiple electrolyser modulesfor producing hydrogen comprising:

-   a. power determination and monitoring means for one or more of    measuring, estimating and predicting the power of the AC electricity    generated by the wind farm;-   b. transmission lines connected to the wind farm for transmitting    the medium to high voltage AC electricity from the wind farm to the    vicinity of the multiple electrolyser modules;-   c. one or more step down n-pulse transformers located proximate to    the multiple electrolyser modules for receiving the medium to high    voltage AC electricity from the transmission lines and transforming    it to low voltage AC electricity;-   d. one or more non-regulated n-pulse rectifiers for receiving the    low voltage AC electricity from the step down transformer and    converting it to non-regulated low voltage DC electricity;-   e. one or more n-pulse DC buses connected to the one or more    non-regulated n-pulse rectifiers for receiving and distributing the    non-regulated low voltage DC electricity;-   f. one or more regulated n-pulse DC-DC converters associated with    each of the multiple electrolyser modules, each of the regulated    n-pulse DC-DC converters connected to at least one of the one or    more n-pulse DC buses, for receiving the non-regulated low voltage    DC electricity from at least one of the one or more n-pulse DC buses    and supplying regulated DC electricity to each of the multiple    electrolyser modules;-   g. one or more electrolyser module controllers connected to the    plurality of electrolyser modules for controlling the plurality of    electrolyser modules;-   h. one or more dispatch controllers connected to the power    determination and monitoring means and the one or more electrolyser    module controllers for monitoring the power determination and    monitoring means and the one or more electrolyser module controller    and for controlling the system for distributing electric power;-   i. one or more alternative loads connected to one or more of the    transmission lines, the low voltage side of the one or more central    step down n-pulse transformers, and for demanding any of the    electric power from the wind farm that is not demanded by the    multiple electrolyser modules;-   j. one or more alternative power sources connected to at least one    of the high voltage side and the low voltage side of the one or more    central step down n-pulse transformer, and said at least one n-pulse    DC bus, for supplying any electric power demanded by the multiple    electrolyser modules that is not supplied by the wind farm. where    n-pulse is one of 6-pulse, 12-pulse, and 24-pulse.

A system for distributing electric power from a wind farm generatingmedium voltage DC electricity to multiple electrolyser modules forproducing hydrogen comprising:

-   a. power determination and monitoring means for at least one of    measuring, estimating and predicting the power of the DC electricity    generated by the wind farm;-   b. transmission lines connected to the wind farm for transmitting    the medium voltage DC electricity from the wind farm to the vicinity    of the multiple electrolyser modules;-   c. one or more step down converters located proximate to the    multiple electrolyser modules for receiving the medium voltage DC    electricity from the transmission lines and converting it to    non-regulated low voltage DC electricity;-   d. one or more DC buses connected to the one or more step down    converters for receiving and distributing the low voltage DC    electricity;-   e. one or more regulated DC-DC converters associated with each of    the multiple electrolyser modules and connected to at least one of    the one or more DC buses, for receiving the non-regulated low    voltage DC electricity from the one or more DC buses and supplying    regulated DC electricity to each of the multiple electrolyser    modules;-   f. one or more electrolyser module controllers connected to the    plurality of electrolyser modules for controlling the plurality of    electrolyser modules;-   g. one or more dispatch controllers connected to the power    determination and monitoring means and the electrolyser module    controllers for monitoring said power determination and monitoring    means and the one or more electrolyser module controllers and for    controlling the system for distributing electric power;-   h. one or more alternative loads connecting one or more of the    transmission lines, the low voltage side of the one or more step    down converters, and the one or more DC buses for demanding any of    the electric power from the wind farm that is not demanded by the    multiple electrolyser modules;-   i. one or more alternative power sources connected to one or more of    the medium voltage side and the low voltage side of the one or more    step down converter, and the one or more DC buses, for supplying any    electric power demanded by the multiple electrolyser modules that is    not supplied by the wind farm.

A method for distributing electric power from a wind farm generatingmedium to high voltage AC electricity to multiple electrolyser modulesfor producing hydrogen comprising the steps of:

-   a. at least one of measuring, estimating and predicting the power of    the AC electricity generated by the wind farm;-   b. estimating power transmission and distribution losses;-   c. transmitting the medium to high voltage AC electricity to the    vicinity of the multiple electrolyser modules;-   d. transforming the AC electricity to low voltage AC electricity    using at one or more step down n-pulse transformers;-   e. converting the low voltage AC electricity to non-regulated low    voltage DC electricity using one or more non-regulated n-pulse    rectifiers;-   f. distributing the non-regulated low voltage DC electricity via one    or more n-pulse DC buses;-   g. receiving and regulating the non-regulated low voltage DC    electricity using one or more regulated n-pulse DC-DC converters    associated with each of the multiple electrolyser modules and    connected to at least one of the one or more n-pulse DC buses, and    supplying regulated DC electricity to each of the multiple    electrolyser modules according to the at least one of measured,    estimated and predicted power of the medium to high voltage AC    electricity generated by the wind farm and estimated power    transmission and conversion losses;-   h. directing any power generated by the wind farm that is not    demanded by the multiple electrolyser modules to one or more    alternative loads;-   i. supplying any electric power demanded by the multiple    electrolyser modules that is not supplied by the wind farm from one    or more alternative power sources.    where n-pulse is one of 6-pulse, 12-pulse, and 24-pulse.

A method for distributing electric power from a wind farm generatingmedium voltage DC electricity to multiple electrolyser modules forproducing hydrogen comprising the steps of:

-   a. at least one of measuring, estimating and predicting the power of    the DC electricity generated by the wind farm;-   b. estimating power transmission and distribution losses;-   c. transmitting the medium voltage DC electricity to the vicinity of    the multiple electrolyser modules;-   d. converting the medium voltage DC electricity to non-regulated low    voltage DC electricity using one or more step down converters;-   e. distributing the non-regulated low voltage DC electricity via one    or more DC buses;-   f. receiving and regulating the non-regulated low voltage DC    electricity using one or more regulated DC-DC converters associated    with each of the multiple electrolyser modules and connected to one    or more of the one or more DC buses, and supplying regulated DC    electricity to each of the multiple electrolyser modules according    to at least one of measured, estimated and predicted power of the    medium voltage DC electricity generated by the wind farm and    estimated power transmission and conversion losses;-   g. directing any power generated by the wind farm that is not    demanded by the plurality of electrolyser modules to one or more    alternative loads;-   h. supplying any electric power demanded by the multiple    electrolyser modules that is not supplied by the wind farm from one    or more alternative power sources.

A method for controlling the distribution of electric power from a windfarm generating at least one of medium to high voltage AC electricityand medium voltage DC electricity to multiple electrolyser modules forproducing hydrogen, comprising the steps of:

-   a. estimating the real time wind farm power available as DC at the    electrolyzer terminals;-   b. determining the number of available electrolyser modules;-   c. measuring the temperature of each electrolyser module;-   d. determining a target current set point for each of the multiple    electrolyser modules based on the estimated available DC power, the    number of available electrolyser modules, and the temperature of    each of the available electrolyser modules;-   e. ramping the DC current supplied by one or more DC-DC power    converters to each of the available electrolyser modules toward the    target current set point;-   f. repeating steps a to e at appropriate time intervals.

DESCRIPTION OF FIGURES

FIG. 1 shows a system for distributing AC electric power generated by awind farm to multiple electrolyser modules in accordance with thepresent invention. Dashed lines indicate control signal carryingconnections; solid lines indicate power carrying connections.

FIG. 2 shows a system for distributing DC electric power generated by awind farm to multiple electrolyser modules in accordance with thepresent invention. Dashed lines indicate control signal carryingconnections; solid lines indicate power carrying connections.

FIG. 3 shows the main control function steps for a system fordistributing electric power generated by a wind farm to multipleelectrolyser modules in accordance with the present invention.

FIG. 4 outlines the first main control block of a method for controllinga system for distributing electric power generated by a wind farm tomultiple electrolyser modules in accordance with the present invention.

FIG. 5 outlines the second main control block of a method forcontrolling a system for distributing electric power generated by a windfarm to multiple electrolyser modules in accordance with the presentinvention.

FIG. 6 outlines the third main control block of a method for controllinga system for distributing electric power generated by a wind farm tomultiple electrolyser modules in accordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS System for Distributing ACElectric Power

A system for distributing AC electric power generated by a wind farm toa plurality of electrolyser modules for producing hydrogen in accordancewith the present invention is shown generally at 1 in FIG. 1. Dashedlines indicate control signal carrying connections; solid lines indicatepower carrying connections. A wind farm 2, with one or more wind turbinegenerators, generates medium to high voltage AC electricity. One or morepower determination and monitoring means 3 are located in or proximateto the wind farm for measuring and/or enabling estimation of and/orenabling prediction of the power of the AC electricity generated by thewind farm. Transmission lines 4 efficiently transmit the medium to highvoltage AC electricity from the wind farm 2 to centralizedtransformation and rectification equipment located in the vicinity ofthe plurality of an electrolyser modules 5. There, one or more centralstep down n-pulse transformers 6 transform the medium to high voltage ACelectricity to low voltage AC electricity. One or more centralnon-regulated n-pulse rectifiers 7 then convert the low voltage ACelectricity from the step down n-pulse transformer to non-regulated lowvoltage DC electricity. One or more n-pulse DC buses 8 then distributethe non-regulated low voltage DC electricity to regulated n-pulse DC-DCconverters 9; one or more n-pulse DC-DC converters are used for each ofthe electrolyser modules 5. The n-pulse DC-DC converters 9 convert thenon-regulated low voltage DC electricity to regulated DC electricity ofthe current-voltage ratio required at any given time by each of thecorresponding electrolyser modules 5. The electrolyser modules 5 utilizethe regulated DC electricity to produce hydrogen gas, and in the case ofwater electrolysis, oxygen gas.

The power dispatch system 1 further comprises one or more electrolysermodule controllers 10 that are connected to the electrolyser modules 5and the n-pulse DC-DC converters 9 for controlling the electrolysermodules, and at least one dispatch controller 11 that is connected tothe one or more power determination and monitoring means 3 and the atleast one electrolyser module controller 10 for implementing systemcontrol as described herein. Preferably, but not necessarily, there isone electrolyser module controller 10 for each of the electrolysermodules 5 and its associated one or more DC-DC converters.

The power dispatch system 1 further comprises means for dealing with apower imbalance between the primary power sources (the wind farm) andprimary power sinks (the electrolyser modules), involving a system ofone or more alternative loads 12 for demanding any of the electric powergenerated by the wind farm 2 that is not demanded by the electrolysermodules 5, one or more alternative power sources 13 for supplying anyelectric power demanded by the electrolyser modules 5 that is notsupplied by the wind farm 2, and one or more fast acting power balancingcontrollers 14 that appropriately activate the one or more alternativeloads and the one or more alternative power sources so as to balance thepower (and reactive power for an AC grid) and thus maintain stablevoltage (and stable frequency for an AC grid). The one or more powerbalancing controllers are connected to the one or more alternative loads12 and the one or more alternative power sources 13, as well asoptionally the transmission lines 4, the one or more n-pulse DC buses 8,and the at least one dispatch controller 11. In the case ofinterconnection to a relatively large utility electrical grid, thefunctions of alternative loads, alternative power sources and powerbalancing controllers are “automatically” carried out by the capacity ofthe large utility electrical grid to absorb and deliver sufficientlevels of power on demand. Alternative loads, alternative power sourcesand power balancing controllers are required on weak electrical gridsthat do not have sufficient on-demand power supply and absorbingcapabilities to maintain stability when power imbalances occur.

Details of the power dispatch system 1 are described below.

The n-pulse equipment in any given system can be one of 6-pulse,12-pulse, or 24-pulse; each 12-pulse or 24-pulse non-regulatedrectifier, DC-bus, or DC-DC converter generally consists of two 6-pulseunits, or four 6-pulse units, respectively. 12-pulse or 24-pulseconfigurations are preferred for use in MW-scale applications forgreatly reduced harmonics and higher power factor versus 6-pulseconfigurations.

The power pathway in accordance with the present invention splits thefunctionality of the power supplies (for example, SCR rectifiers) in aconventional power pathway into two discrete functions; AC-DC powerconversion and DC power regulation (DC-DC power conversion). Separationof the two functionalities enables “centralization” of the AC-DC powerconversion equipment, that is, use of a single larger and more costeffective AC-DC power converter. Non limiting examples of suitablehardware are diode rectifiers for AC-DC power conversion (i.e., the oneor more central non-regulated n-pulse rectifiers 7), and choppers for DCpower regulation (i.e., the one or more n-pulse DC-DC converters usedfor each of the electrolyser modules 5); 12-pulse or 24 pulse equipmentand connecting buses are preferred for MW-scale power systems. Since SCRrectifiers are not used, the one or more central step down n-pulsetransformers 6 can be single stage transformers.

The combination of non-regulated diode rectifiers 7 and regulated DC-DCconverters 9 provides advantages versus SCR rectifiers such as goodefficiency over a wide range of operating power (“flat efficiency”),good power factor and low harmonics. These characteristics also allowfor use of a more conventional transformer and with more effective andefficient single stage step down from high voltage. Although SCRrectifiers have better efficiency near rated output compared with otherpower supplies that have more than one conversion stage, at lower poweroutputs the harmonics generated by slicing up of the AC waveform causesheating and losses in the transformer. The use of 12-pulse or 24-pulsediode rectifiers and downstream DC buses is preferred for MW-scale powersystems.

Chopper type DC to DC converters can be used as the one or more DC-DCconverters 9 to provide regulated DC electricity of the required voltageand current to the multiple electrolyser modules 5. In the case of a12-pulse configuration, which is preferred for MW-scale applications, atleast one 12-pulse chopper (consisting of two 6-pulse choppers) isrequired for each electrolyser cell module for independent powercontrol. Use of the same DC-DC power converter 9 to feed power tomultiple electrolyser modules 5 can be considered, provided that thepossibility of uneven current sharing between the multiple electrolysermodules can be tolerated.

The at least one dispatch controller 11 may be a PLC or similar device.The robustness and responsiveness of PLC's makes them well suited tothis application. The at least one dispatch controller monitors the oneor more electrolyser module controllers 10, which may also be PLC's orsimilar devices, for data, alarms and faults; it also monitors the oneor more power determination and monitoring means 3 to acquire real timeor predicted wind power data. In addition to direct power measurements,other approaches to estimating or predicting wind power as are known inthe art also can be used. For example, wind power or wind speed can bemeasured at each wind turbine and the multiple measurements can be usedto provide total estimated real time or predicted wind power for thewind farm. The at least one dispatch controller uses the acquired datato control the power dispatch system by implementing the controlstrategy described herein. The at least one dispatch controller may havea redundant processor for fail-safe operation and may communicate withthe one or more electrolyser module controllers and with the one or morepower determination and monitoring means over a redundant communicationsnetwork.

One electrolyser module controller 10 per electrolyser module 5 is shownin FIG. 1 as a preferred, but not necessarily required approach. Theelectrolyser module controllers monitor and control all the functions ofthe electrolyser modules and the DC-DC converters 9. In addition to thestandard controller function, a separate safety critical relay systemmay also be used to monitor safety critical conditions that wouldwarrant shutdown of the cell module and its power supply during out ofbounds operation. This separate safety system ensures reliable shutdownshould the controllers fail.

The one or more alternative power sources 12 may include but are notlimited to a utility electrical grid, a local electrical grid, powergenerator sets, or energy storage and electricity regeneration equipmentsuch as flywheel, batteries (including redox flow batteries) andcompressed air energy systems. The one or more alternative power sources12 may be connected to one or more of the medium voltage or low voltagesides of the one or more central step down DC-DC converters 6, or to theone or more DC buses 8. The one or more alternative power sources 13 mayinclude but are not limited to a utility electrical grid, a localelectrical grid, power generator sets, or energy storage and electricityregeneration equipment such as flywheels, batteries (including redoxflow batteries) and compressed air energy systems. In cases in which thewind-hydrogen system is providing hydrogen to an associated hydrogenuser such as a chemical plant or refinery, the associated hydrogen usermay provide some or all of the required alternative loads andalternative power sources.

The one or more alternative loads 12 may include but are not limited toa utility electrical grid, a local electrical grid, dump resistiveloads, or energy storage and electricity regeneration equipment such asflywheels, batteries (including redox flow batteries) and compressed airenergy systems. The one or more alternative loads 12 may be connected toone or more of the transmission lines 4, the low voltage side of the oneor more central step down n-pulse transformers 6, and the one or moren-pulse DC buses 8. The one or more alternative power sources 13 mayinclude but are not limited to a utility electrical grid, a localelectrical grid, power generator sets, or energy storage and electricityregeneration equipment such as flywheels, batteries (including redoxflow batteries) and compressed air energy systems. In cases in which thewind-hydrogen system is providing hydrogen to an associated hydrogenuser such as a chemical plant or refinery, the associated hydrogen usermay provide some or all of the required alternative loads andalternative power sources.

Alternative loads 12 and alternative power sources 13 may be one or moreof medium to high voltage AC, low voltage AC, or DC. In the case of12-pulse and 24-pulse equipment, any alternative loads and/oralternative power sources connected to the low voltage side of the oneor more central step down n-pulse transformers 6 or the DC buses must bebalanced for each of the two sides for 12-pulse configurations, and eachof the four sides for 24-pulse configurations. DC loads and powersources might have faster response if AC loads and power sources must besynchronized to an electrical grid.

Normal wind excursions such as sudden drops in wind power or sudden lossof a single wind turbine generator in a relatively large wind farm(nominal wind power of, for example, 50 MW or more) will perturb thewind hydrogen system 1 and will require the employment of one or morealternative power sources 13 to make up the short-term power differencebetween the power demanded by the electrolyser modules 5 and the powersupplied by the wind farm 2. The magnitude and duration of the powerdifference will depend on the magnitude and duration of the wind powerloss and the time delay between wind power measurement and currentcontrol to the electrolyser modules. The time delay between powermeasurement and current control preferably is less than one second.

However, large power differences that would occur from the suddenshutdown of large numbers of wind turbine generators, such as during apower grid fault, would necessitate alternative power sources 13 of highrating approaching that of the total wind farm rating. This clearly isnot a desirable or practical solution. Therefore, for sudden large windpower losses another means must be available to quickly bring theelectrolyzer modules off line. In the most basic case of the entire windfarm shutting down at once, either a shutdown signal from the wind farm2, the one or more power determination and monitoring means 3, or apower loss detection relay can be used to send a shutdown signal to theelectrolyzer plant. This capability also could be implemented throughthe dispatch controller 11 if the controller is fast enough; however, ingeneral, implementation through a faster means such as through ahardwire circuit or as part of the power balancing controller 14function is preferred.

If only parts of the wind farm shut down at once leaving a significantpower source still active, then only an equivalent part of theelectrolyzer plant can be shut down or “shed”. This capability requiresa special design as part of the power balancing controller to properlymaintain the power balance either through bringing on power sources orshedding loads such as the electrolyzer modules.

Sudden wind gusts of large magnitude also can imbalance the powerdispatch system, sometimes up to the rating of the wind farm. Theimbalance will be maintained as long as the electrolyzer modules powerramp rate cannot keep up with the wind power ramp rate. The switching onof any non-operating electrolyzer modules to keep up with this rise inwind power will only increase the time to regain power balance. Anappropriately sized large alternative load, although required for veryshort periods of time, may be unsuitable with respect to size and cost.Modern wind turbine generators provide the means to curtail (reduce)their output automatically or on demand, and this feature may well berequired for weak grids in order to avoid a requirement for very largealternative loads. Modern wind speed prediction algorithms used in windturbine generator controls may also help to provide highly responsivecurtailing of wind turbine generator power.

Wind power gusts are not the only potential source of power imbalanceson the grid. The close tracking of wind power by the electrolysermodules requires accurate and timely wind power determinations(measurements/estimates/predictions) to be translated into accuratepower settings for the electrolyser modules. In practice, some errors inthe power measurements may occur through calibration errors ininstruments and inaccuracy in estimating losses/conversions between thepoint of wind power measurement and the electrolyser modules DC bus.Also, time delay between measuring/estimating/predicting wind power andelectrolyser modules current control will add to this error. Theseerrors will be translated into power imbalances on a weak grid that mustbe corrected through the alternative load and alternative power sourcecontrol system.

Error mitigation approaches can potentially reduce these errors andlower the ratings and costs of the alternative loads and sources. Oneerror mitigation approach is to utilize power imbalance readingsdetermined by the power balancing controller and feed this informationback to the dispatch controller so that it can adjust the power settingsto the electrolyser modules. The power balancing controller must havethe capability to translate frequency (in the case of AC grid) orvoltage (in the case of DC grid) excursions into power imbalance levels(positive for excess power on the grid and negative for excess draw onthe grid).

One potential implementation of this error mitigation approach is to seta threshold power level, and whenever the power balancing controllermeasures an imbalance on the grid above this threshold level, it sendsan interrupt signal to the dispatch controller to adjust the powerlevels to the electrolyser modules by the threshold power level in thedirection to correct the imbalance, as long as the electrolyser modulecurrent rating and maximum ramp rate are maintained. The optimumthreshold power level can be determined through computer simulation.This method does not require an accurate determination of the powerimbalance level. Computer simulation results from such a “step typeerror mitigation” method are shown in the Examples below.

Another potential implementation of the error mitigation approach is tocontinuously determine the actual power imbalance (either positive ornegative) on the grid and feed these data to the dispatch controller soit can adjust the power settings to the electrolyser modulesproportionately. This potential implementation requires accurate powerimbalance determinations; otherwise, its own introduction of error intothe control strategy will not provide any improvement.

If an error mitigation method is employed, then the power balancingcontroller 14 will send a signal to the dispatch controller 11. In thecase of a step type error mitigation method, a digital signal is sent tothe dispatch controller when a threshold power setting is exceeded ineither positive or negative power imbalance. In the case of thecontinuous error mitigation method, an analog signal proportional to thepositive or negative power imbalance is sent to the dispatch controller.

In the case of interconnection to a relatively large utility electricalgrid, the functions of alternative loads and alternative power sourcesare “automatically” carried out by the capacity of the large utilityelectrical grid to absorb and deliver sufficient levels of power ondemand. At the opposite extreme, in the case where the wind-hydrogensystem is a stand-alone system, active power management as is known inthe art is required to control and appropriately utilize the requiredlevel of alternative loads or alternative power sources to correct anypower imbalance. The power balancing controller 14 for active powermanagement must be fast and dynamic with millisecond response and meansto measure frequency and voltage variance. In the case of remote utilityelectrical grids, the remote utility electrical grid may “automatically”provide some of the functions of alternative loads and alternative powersources, and the remote utility electrical grid may have an active powermanagement system.

Thus, distribution of electric power from a wind farm for generatingmedium to high voltage AC electricity to multiple electrolyser modulesfor producing hydrogen generally involves the following steps: (a)estimating in real time and/or predicting the power of the ACelectricity generated by the wind farm; (b) transmitting medium to highvoltage AC electricity to the multiple electrolyser modules; (c)transforming the medium to high voltage AC electricity to low voltage ACelectricity using one or more step down transformers; (d) converting thelow voltage AC electricity to non-regulated low voltage DC electricityusing one or more non-regulated rectifiers; (e) distributing thenon-regulated low voltage DC electricity via one or more DC buses; (f)receiving and regulating the non-regulated low voltage DC electricityusing one or more regulated DC-DC converters associated with each of themultiple electrolyser modules and connected to at least one of the oneor more DC buses, and supplying regulated DC electricity to each of themultiple electrolyser modules according to the measured power of the ACelectricity generated by the wind farm and estimated power transmissionand conversion losses; (g) directing any power generated by the windfarm that is not demanded by the multiple electrolyser modules to one ormore alternative loads; and, (h) supplying any electric power demandedby the multiple electrolyser modules that is not supplied by the windfarm from one or more alternative power sources.

System for Distributing DC Electric Power

A system for distributing DC electric power generated by a wind farm toa plurality of electrolyser modules for producing hydrogen in accordancewith the present invention is shown generally at 1 in FIG. 2. Dashedlines indicate control signal carrying connections; solid lines indicatepower carrying connections. The wind farm 2, with one or more windturbine generators, generates medium voltage DC electricity. One or morepower determination and monitoring means 3 are located in or proximateto the wind farm for measuring and/or enabling estimation of and/orenabling prediction of the power of the medium voltage DC electricity.The transmission lines 4 efficiently transmit the medium voltage DCelectricity from the wind farm to the vicinity of the plurality of theelectrolyser modules 5. There, one or more central step down DC-DCconverters 6 convert the medium voltage DC electricity to low voltage DCelectricity. One or more DC buses 7 then distribute the non-regulatedlow voltage DC electricity to regulated DC-DC converters 8; one or moreDC-DC converters are used for each of the electrolyser modules 5. TheDC-DC converters 8 convert the non-regulated low voltage DC electricityto regulated DC electricity of the voltage-current ratio required at anygiven time by each of the corresponding electrolyser modules. Theelectrolyser modules 5 utilize the regulated DC electricity to producehydrogen gas, and in the case of water electrolysis, oxygen gas.

The power dispatch system 1 further comprises one or more electrolysermodule controllers 9 that are connected to the electrolyser modules 5and the respective DC-DC converters 8 for controlling the electrolysermodules, and at least one dispatch controller 10 that is connected tothe power determination and monitoring means 3 and the electrolysermodule controllers 9 for implementing system control as describedherein.

The power dispatch system 1 further comprises means for dealing withpower imbalance between the primary power sources (the wind farm) andprimary power sinks (the electrolyser modules) involving a system of oneor more alternative loads 11 for demanding any of the electric powergenerated by the wind farm 2 that is not demanded by the electrolysermodules 5, or one or more alternative power sources 12 for supplying anyelectric power demanded by the electrolyser modules 5 that is notsupplied by the wind farm 2, and one or more fast acting power balancingcontrollers 13 that appropriately activate the one or more alternativeloads and the one or more alternative power sources to balance the powerand thus maintain stable voltage. The one or more power balancingcontrollers 13 are connected to the one or more alternative loads 11 andthe one or more alternative power sources 12, as well as optionally thetransmission lines 4, and the at least one dispatch controller 10. Inthe case of interconnection of a medium voltage DC transmission line toa relatively large utility electrical grid, the functions of alternativeloads and alternative power sources are “automatically” carried out bythe capacity of the large utility electrical grid to absorb and deliversufficient levels of power on demand. Alternative loads, alternativepower supplies and power balancing controllers are required on weakelectrical grids that do not have sufficient on-demand power supply andabsorbing capabilities to maintain stability when power imbalancesoccur.

Details of the power dispatch system 1 are described below.

Wind turbine generators producing DC power, although currently lesscommon than those producing AC power, are commercially available. Theindividual DC wind turbine generators typically each have a rectifierthat delivers low voltage DC power to a DC-DC boost converter. The boostconverter boosts the voltage from low to medium level. The boostconverters for individual wind turbine generators feed into a commonmedium voltage DC transmission line. The DC transmission line can beburied and routed to the electrolyser modules. At the electrolysermodules location, the one or more central DC-DC converters 7 may be, butare not limited to, buck converters that bring the voltage back down toa low voltage on a common DC bus. The one or more regulated DC-DCconverters 8 may be, but are not limited to, individual chopper powersupplies that deliver regulated DC electricity from the DC bus to eachof the electrolyser modules 5. At least one DC-DC converter is requiredfor each electrolyser cell module for independent power control. Use ofthe same DC-DC power converter 8 to feed power to multiple electrolysermodules 5 can be considered, provided that the possibility of unevencurrent sharing can be tolerated.

The dispatch controller 10 may be a PLC or a similar device. Therobustness and responsiveness of PLC's makes them well suited to thisapplication. The dispatch controller monitors the electrolyser modulescontrollers 9, which may also be PLC's or similar devices, for data,alarms and faults; it also monitors the one or more power determinationand monitoring means 3 to acquire real time or predicted wind powerdata. In addition to direct power measurements, other approaches toestimating or predicting wind power as are known in the art also can beused. For example, wind power or wind speed can be measured at each windturbine and the multiple measurements can be used to provide totalestimated real time or predicted wind power for the wind farm. Thedispatch controller uses the acquired data to control the power dispatchsystem by implementing the control strategy described herein. Thedispatch controller may have a redundant processor for fail-safeoperation and may communicate with the electrolyser module controllersand with the power determination and monitoring means over a redundantcommunications network.

One electrolyser module controller 9 per electrolyser module 5 is shownin FIG. 1 as a preferred, but not necessarily required approach. Theelectrolyser module controllers control all the functions of theelectrolyser modules and the DC-DC converters 8. In addition to thestandard controller function, a separate safety critical relay systemmay also be used to monitor safety critical conditions that wouldwarrant shutdown of the cell module and its power supply during out ofbounds operation. This separate safety system ensures reliable shutdownshould the controllers fail.

The one or more alternative loads 11 may include but are not limited toa utility electrical grid, a local electrical grid, dump resistiveloads, or energy storage and electricity regeneration equipment such asflywheels, batteries (including redox flow batteries) and compressed airenergy systems. The one or more alternative loads 11 may be connected toone or more of the transmission lines 4, the low voltage side of the oneor more central step down DC-DC converters 6, and the one or more DCbuses 7. The one or more alternative power sources 12 may include butare limited to a utility electrical grid, a local electrical grid, powergenerator sets, or energy storage and electricity regeneration equipmentsuch as flywheels, batteries (including redox flow batteries) andcompressed air energy systems. The one or more alternative power sources12 may be connected to one or more of the medium voltage or low voltagesides of the one or more central step down DC-DC converters 6, or to theone or more DC buses 7. The one or more alternative power sources 12 mayinclude but are not limited to a utility electrical grid, a localelectrical grid, power generator sets, or energy storage and electricityregeneration equipment such as flywheels, batteries (including redoxflow batteries) and compressed air energy systems. The one or morealternative power sources 12 may be connected to one or more of themedium voltage or low voltage sides of the one or more central step downDC-DC converters 6, or to the one or more DC buses 7. In cases in whichthe wind-hydrogen system is providing hydrogen to an associated hydrogenuser such as a chemical plant or refinery, the associated hydrogen usermay provide some or all of the required alternative loads andalternative power sources.

Alternative loads 11 and alternative power sources 12 are DC, except inthe case in which the alternative loads and alternative power sourcesare provided by an AC grid (utility grid or local grid).

Normal wind excursions such as sudden drops in wind power or sudden lossof a single wind turbine generator in a relatively large wind farm(nominal wind power of, for example, 50 MW or more) will perturb thewind hydrogen system 1 and require the employment of one or morealternative power sources 12 to make up the short-term power differencebetween the power demanded by the electrolyser modules 5 and the powersupplied by the wind farm 2. The magnitude and duration of the powerdifference will depend on the magnitude and duration of the wind powerloss and the time delay between wind power measurement and currentcontrol to the electrolyser modules. The time delay between powermeasurement and current control preferably is less than one second.

However, large power differences that would occur from the suddenshutdown of large numbers of wind turbine generators, such as during apower grid fault, would necessitate alternative power sources 12 of highrating approaching that of the total wind farm rating. This clearly isnot a desirable or practical solution. Therefore, for sudden large windpower losses another means must be available to quickly bring theelectrolyser modules off line. In the most basic case of the entire windfarm shutting down at once, either a shutdown signal from the wind farm2, the one or more power and/or wind speed measuring and monitoringmeans 3, or a power loss detection relay can be used to send a shutdownsignal to the electrolyser plant. This capability also could beimplemented through the dispatch controller 10 if the controller is fastenough; however, in general implementation through a faster means suchas through a hardwire circuit or as part of the power balancingcontroller 13 function is preferred.

If only parts of the wind farm shut down at once leaving a significantpower source still active, then only an equivalent part of theelectrolyser plant can be shut down or “shed”. This capability requiresa special design as part of the power balancing controller to properlymaintain the power balance either through bringing on power sources orshedding loads such as the electrolyser modules.

Sudden wind gusts of large magnitude also can imbalance the powerdispatch system, sometimes up to the rating of the wind farm. Theimbalance will be maintained as long as the electrolyser modules powerramp rate cannot keep up with the wind power ramp rate. The switching onof any non-operating electrolyser modules to keep up with this rise inwind power will only increase the time to regain power balance. Anappropriately sized large alternative load, although required for veryshort periods of time, may be unsuitable with respect to size and cost.Modern wind turbine generators provide the means to curtail (reduce)their output automatically or on demand, and this feature may well berequired for weak grids in order to avoid a requirement for very largealternative loads. Modern wind speed prediction algorithms used in windturbine generator controls may also help to provide highly responsivecurtailing of wind turbine generator power.

If an error mitigation method is employed, then the power balancingcontroller 13 will send a signal to the dispatch controller 10. In thecase of a step type error mitigation method, a digital signal is sent tothe dispatch controller when a threshold power setting is exceeded ineither positive or negative power imbalance. In the case of thecontinuous error mitigation method, an analog signal proportional to thepositive or negative power imbalance is sent to the dispatch controller.

In the case of interconnection to a relatively large utility electricalgrid, the functions of alternative loads and alternative power sourcesare “automatically” carried out by the capacity of the large utilityelectrical grid to absorb and deliver sufficient levels of power ondemand. At the opposite extreme, in the case where the wind-hydrogensystem is a stand-alone system, active power management as is known inthe art is required to control and appropriately utilize the requiredlevel of alternative loads or alternative power sources to correct anypower imbalance. The power balancing controller 13 for active powermanagement must be fast and dynamic with millisecond response and meansto measure voltage variance. In the case of interconnection to remoteutility electrical grids, the remote utility electrical grid may“automatically” provide some of the functions of alternative loads andalternative power sources, and the remote utility electrical grid mayhave an active power management system.

Thus, distribution of electric power from a wind farm for generatingmedium voltage DC electricity to multiple electrolyser modules forproducing hydrogen generally involves the following steps: (a)estimating in real time and/or predicting the power of the DCelectricity generated by the wind farm; (b) transmitting the mediumvoltage DC electricity to the plurality of electrolyser modules; (c)converting the medium voltage DC electricity to non-regulated lowvoltage DC electricity using at least one step down converter; (d)distributing the non-regulated low voltage DC electricity via at leastone DC bus; (e) receiving and regulating the non-regulated low voltageDC electricity using at least one regulated DC to DC converterassociated with each of the plurality of electrolyser modules andconnected to at least one of the at least one DC buses, and supplyingregulated DC electricity to each of the multiple electrolyser modulesaccording to the measured power of the DC electricity generated by thewind farm and estimated power transmission and conversion losses; (f)directing any electric power generated by the wind farm that is notdemanded by the multiple electrolyser modules to one or more alternativeloads; and, (g) supplying any electric power demanded by the multipleelectrolyser modules that is not supplied by the wind farm from one ormore alternative power sources.

Currently, AC transmission is preferred over DC transmission for use inthe present invention based on efficiency, cost, reliability and proventechnology. DC to DC power conversion and regulation technology willneed to develop further to improve efficiency, costs and reliabilitybefore DC power transmission becomes a practical option. However, longtransmission distance between the wind farm and the electrolyser modulescould ultimately make DC power transmission more cost effective than ACtransmission for transmission distances of 50 km or more.

Power Dispatch System Control and Load Matching to Wind Farm Power

A method for controlling the distribution of electric power from a windfarm for generating at least one of medium to high voltage ACelectricity and medium voltage DC electricity to a plurality ofelectrolyser modules for producing hydrogen is outlined in FIG. 3. Thecontrol method consists of the steps of: (a) estimating the real timeavailable DC power from the wind farm; (b) determining the number ofactive electrolyser modules (defined as electrolyser modules not underalarm or fault condition); (c) measuring the voltage of eachelectrolyser module; (d) determining the target current set point foreach of said plurality of electrolyser modules based on the estimatedavailable DC power from the wind farm, the number of active electrolysermodules, and the voltage of each of said active electrolyser modules;and, (e) ramping the DC current supplied by the DC-DC power convertersto each of the available electrolyser modules toward the target currentset point. Steps (a) to (e) are repeated at appropriate time intervals.Thus, the operating power of the electrolyser modules is continuallymoving toward a target set point power, determined by estimating thereal time available power generated by the wind farm, as well as thenumber of available electrolyser modules and their estimatedperformance. Each electrolyser module will have a characteristiccurrent-voltage curve at any given operating temperature; consequently,the operating power of the electrolyser modules is set by setting theoperating current, which in turn sets the operating voltage.

Computer simulation modeling using actual wind farm power generationdata has shown that time intervals for repetition of steps (a) to (e) ofthe order of 1 to 10 seconds may be sufficient for systems with windfarms of 51 MW or 150 MW; as in any “integration” type process, theshorter the time interval, the better the control will be, and in thiscase, the better the power tracking and energy capture will be. Inpractice, the lower limit of the time interval will be set by theresponse of the controllers and the power measuring devices, and thenumber of commands; several hundred commands could be required for a 150MW wind farm. For several hundred commands, the time interval could beup to several hundred ms. Accordingly, an approximate practical “best”range for the time interval for repetition of steps (a) to (e) may be,for example, 0.7-1 seconds for a 150 MW wind farm. Appropriate timeintervals can be estimated in a similar manner for systems with windfarms of different nominal output powers.

The current ramp rate for each electrolyser module is also expected tobe an important parameter. Computer simulation modeling using actualwind farm power generation data indicates that current ramp rates of atleast about 0.5% of the nominal power rating, or at least about 0.25% ofthe peak power rating of the electrolyser modules, result in capture ofvery high percentages of the wind power generated. The magnitude ofthese current ramp rates corresponds to at least about 19 A/s. Thus, theuse of electrolyser modules capable of achieving high current ramp ratesis preferred. Allowable current ramp rates may vary with operatingtemperature. The allowable current ramp rate as a function of operatingtemperature also can be expected to vary for different electrolysermodule designs.

The electrolyser modules have an operating current window that isdefined by the nominal current (power) rating at the high end, and bythe minimum current (power) turn down at the low end. The nominalcurrent (power) rating of an electrolyser module is determined by theratings of internal functional components, and by its ability togenerate gases with good fluids circulation, good gas-liquid separation,and without overheating. The minimum current turn down capability of anelectrolyser module is determined by its ability to generate hydrogengas with good purity, as well as the operating efficiency curve of theassociated power conversion equipment. Preferably, the operating currentshould not extend outside of the operating current window for anyextended periods. Accordingly, use of electrolyser modules with a wideoperating current window, for example, in terms of current density,0.1-1.0 A/cm², is advantageous. An appropriate large scale electrolysermodule design with a wide operating current window is described inco-pending application, which is incorporated herein in its entirety.

Another important aspect of the control strategy that facilitates goodwind power tracking and high energy capture is distribution of the totalpower evenly over all the available electrolyser modules. This approachminimizes the magnitude of power fluctuations seen by each electrolysermodule, thereby maximizing power tracking capability for any givencurrent ramp rate. The approach also maximizes “head room” toaccommodate sudden wind power increases, and further, maintains thecurrent set points as low as possible for each electrolyser module,thereby maximizing the efficiency of the electrolyser modules.

Tracking of low power generated by the wind farm can be improved throughextending the effective overall operating current window downward byturning off one or more electrolyser modules after a time delay if thecurrent set point is less than an established low minimum current.(Here, an “established” parameter refers to a fixed parameter in thecontrol logic that is set by the designer and used throughout thecontrol.) If the current set point increases above an established highminimum current, one or more of the electrolyser modules that wereturned off is turned back on after a time delay. The time delays and therange between the established low minimum current and the establishedhigh minimum current help to minimize instances in which electrolysermodules are turned on and off with high frequency. In this regard, therun times of the multiple electrolyser modules are evened out (byseparate control logic); that is, they are made as equal as possibleover time. Further, any on-off operation of each of the multipleelectrolyser modules is spaced out over time (by other separate controllogic). Electrolyser modules may also be operated at minimum current ifan alarm condition(s) is encountered. Alarm conditions may include, butare not limited to, high or low temperature, pressure or liquid level.The purpose of operating any alarmed electrolyser modules at minimumcurrent is to provide a safe operating condition that could “self heal”and allow the electrolyser module to return to normal operating status.Any electrolyser modules in alarm condition are reinstated to normaloperation if the alarm condition(s) corrects itself. If the alarmcondition(s) does not correct itself, the electrolyser module(s)condition is elevated to fault state, and the electrolyser module(s) isturned off.

Control Function Steps Description

The main control function steps are outlined in FIG. 3. There are threemain control blocks, each of which is described below in terms of (i)real time data inputs; (ii) characteristic data; (iii) control outputs;and, (iv) control logic and control actions.

Control block 1 is outlined in FIG. 4. In control block 1, the real timeavailable DC wind power is estimated. The real time data input aremeasured, estimated, or predicted total wind farm output power atregular intervals, for example, every second or more frequently—(thefiner the time interval, the better the power tracking will be).Characteristic data required, preferably but not necessarily provided inthe form of a lookup table, are the efficiency of the power conversionpath from the point of wind farm power determination to regulated DCpower input to the electrolyser modules, as a function of power level.The control logic is: total DC power input to electrolyser modules=windfarm output power×efficiency of the power conversion path.

If an error mitigation method is employed, then the wind farm outputpower is adjusted by an amount determined by a signal from the powerbalancing controller. In the case of a step type error mitigationmethod, a digital signal will adjust the value of the wind farm outputpower by the threshold power positive or negative depending on thedirection of the imbalance. In the case of the continuous errormitigation method, an analog signal proportional to the positive ornegative power imbalance will adjust the wind farm output power by thatamount.

Control block 2 is outlined in FIG. 5. In control block 2, electrolysermodule current target set points are determined for the availableelectrolyser modules and the electrolyser modules are ramped toward thetarget set points. The real time data input are: (i) real time DCvoltage of each electrolyser module; (ii) optionally, real timetemperature of each electrolyser module; and (iii) alarm, fault and runstatus of each electrolyser module. Characteristic data are: (i) theminimum allowable turn down current for the electrolyser modules; (ii)the on transition occurrence for each electrolyser module; (iii) themaximum current setting for the electrolyser modules; (iv) the on'offstate for each electrolyser module; (v) appropriate current ramp rates;and optionally, (vi) voltage versus current versus temperature for theelectrolyser modules. The control outputs are the current set point toeach electrolyser module.

The control logic for control block 2 is: target power per activeelectrolyser module=(total DC power−power to alarmed electrolysermodules)/(number of active electrolyser modules), where the activeelectrolyser modules are those that are operating and are not in analarm or fault condition; that is, number of active electrolysermodules=(total number of electrolyser modules)−(number of alarmed andfaulted electrolyser modules)−(number of fully off electrolysermodules). Corresponding control actions are as follows: (i) electrolysermodules in alarm state will operate fixed at minimum turn down setting;(ii) time out alarm state actions are (a) if recovered, then clear alarmstatus, and (b) if not recovered, then elevate to fault state; (iii)electrolyser modules in fault state will always be off; (iv) the targetpower will be divided evenly between available electrolyser modules,compensating for alarmed electrolyser modules running at the minimumturn down current; (v) determine the target current set point for eachelectrolyser module from the target power divided by the voltage—ifaccurate voltage versus current versus temperature data are available,they can be used to estimate the voltage at the next currentiteration—otherwise, actual electrolyser module voltages will be used;(vi) ramp the current of each available electrolyser module toward thetarget current—the current cannot exceed the maximum electrolyser modulecurrent. The allowable current ramp rate for the electrolyser moduleoperating temperatures also may be checked or determined.

Control block 3 is outlined in FIG. 6. In control block 3, electrolysermodules are turned on or off based on the current setting, the operatingpressure, and on-off and run time tables for the electrolyser modules.The real time data input are the operating current and pressure of eachelectrolyser module. Characteristic data are: (i) the minimum allowableturn down current for the electrolyser modules; (ii) the maximumallowable turn down current for the electrolyser modules; (iii) the timedelay to decide an on transition of one or more electrolyser modules;(iv) the time delay to decide an off transition of one or moreelectrolyser modules; (v) the acceptable operating pressure range; (vi)the on or off state of each electrolyser module; and, (vii) the laston-off transition time and accumulated run time for each electrolysermodule. The control outputs are control of the on-off transitions ofeach electrolyser module.

The control logic and control actions for control block 3 are asfollows. If the actual operating current of an electrolyser module risesabove an established high minimum current, then: (i) wait the ontransition delay; (ii) if the current set point is still above theestablished high minimum value, then turn on one or more electrolysermodules; (iii) if the operating pressure of one or more electrolysermodules is below the acceptable operating pressure range, then choosethose electrolyser modules to be turned on; (iv) otherwise, choose whichelectrolyser modules to turn on based on minimum run time and thelongest time since the last on-off transition. If the actual operatingcurrent of an electrolyser module falls below an established low minimumcurrent, then: (i) wait the off transition time delay; (ii) if thecurrent is still below the established low minimum current, then turnoff one or more electrolyser modules; (iii) choose which electrolysermodules to turn off based on maximum run time and the longest time sincethe last on-off transition; (iv) keep electrolyser modules with lowpressure on until the pressure reaches the acceptable operating pressurerange.

Further, a control interface would have access to real time operatingdata for the system, including: (i) the total AC wind farm power andcorresponding DC power after losses; (ii) the actual total DC power tothe electrolyser modules; (iii) the difference between the wind farmcorresponding DC and actual DC power to the electrolyser modules,indicating the level of success of power tracking; (iv) accumulatedenergy figures for (i) to (iii). A control interface also would haveaccess to real time operating data for each electrolyser module,including: (i) on-off, alarm or fault status for each electrolysermodule; (ii) alarm and fault conditions detailed as to cause; (iii)on-off transition times and run times; (iv) operating current, voltage,temperature and pressure.

Example 1

A power distribution system according to the present invention wassimulated by a computer model, using data from a nominal 51 MW windfarm. Second-by-second data for one week, high yield and low yieldperiods were used. The power transmission and conversion path efficiencywas assumed to be flat at 97%. The electrolyser modules were rated at 3MW maximum (7,500 A and nominal 400 V). The number of electrolysermodules used was 17. The cell voltage was assumed to be 2.0 V/cell atall operating currents as an approximation. The electrolyser modulecurrent ramp rate was 0.5% of the maximum current per second, or 37.5A/s based on the maximum current of 7,500 A. The electrolyser module lowminimum current was 375 A (5% of the maximum current) and the highminimum current was 562.5 A (7.5% of the maximum current). The delaytime for a decision to turn an electrolyser module on or off was 10seconds. The electrolyser modules were turned on or off one at a time.The time interval for repetition of the basic control algorithm was onesecond. In this initial modeling, the effects of power measurement delayand error were neglected.

The power capture for the high yield week was generally about 98% orbetter at any given time, and the cumulative energy capture was 99.96%.(These values are separate from the 3% losses associated with the powertransmission and conversion path.) The electrolyser modules wereoperating 97% of the time on average during the high yield week, with anaverage on-off transition frequency of 21 hours. The power capture forthe low yield week was generally about 99.5% or better at any giventime, and the cumulative energy capture was 99.74%. The electrolysermodules were operating 40% of the time on average during the low yieldweek, with an average on-off transition frequency of 2 hours.

Example 2

Next, the effect of varying the current ramp rate in the computer modelsimulation of Example 1 was investigated. The effects of powermeasurement delay and error were again neglected. The results are shownin Table 1. Current ramp rates greater than or equal to 0.25% of themaximum current rating of 7500 A resulted in overall energy capture of99.5% or better; ramp rates greater than or equal to 0.5% of the maximumcurrent rating resulted in overall energy capture of 99.7% or better;and, ramp rates of 1% resulted in overall energy capture of 99.85% orbetter.

TABLE 1 Effect of Current Ramp Rate on Capture of Energy from a 51 MWWind Farm During High Yield and Low Yield Weeks Current Ramp Rate (A/s)1.88 3.75 7.5 18.75 37.5 75 Current Ramp Rate (% 0.025% 0.05% 0.1% 0.25%0.5% 1% of Maximum Current) % Energy 94.65 97.46 98.91 99.54 99.74 99.85Capture—Low Yield Week % Energy 98.86% 99.44 99.76 99.92 99.96 99.97Capture—High Yield Week

Example 3

Next, the effect of varying the frequency of estimating the real timeavailable DC power from the wind farm in the computer model simulationof Examples 1 and 2 was investigated for a current ramp rate of 0.5% ofthe maximum current rating of 7,500 A. The results are shown in Table 2.The higher the estimation frequency, the lower the losses. Higher losseswere observed for the low yield week than for the high yield week.

TABLE 2 Effect of Frequency of Estimating the Real Time Available DCPower from a 51 MW Wind Farm during High Yield and Low Yield WeeksFrequency of Estimation (s) 1 2 4 8 16 % Loss of Wind Energy - 0.26 0.390.52 0.72 1.01 Low Yield Week % Loss of Wind Energy - 0.04 0.10 0.150.23 0.32 High Yield Week

Example 4

Next, the computer simulation model was extended to cover a full year.Second-by-second data for a 51 MW wind farm over two consecutive 6 monthperiods were used. The power transmission and conversion path efficiencywas assumed to be flat at 97%. The electrolyser modules were rated at 3MW maximum (7,500 A and nominal 400 V). The number of electrolysermodules used was 17. The cell voltage was assumed to be 2.0 V/cell atall operating currents as an approximation. The electrolyser modulecurrent ramp rate was 0.5% of the maximum current per second, or 37.5A/s based on the maximum current of 7,500 A. The electrolyser module lowminimum current was 375 A (5% of the maximum current) and the highminimum current was 562.5 A (7.5% of the maximum current). The delaytime for a decision to turn an electrolyser module on or off was 10seconds. The electrolyser modules were turned on or off one at a time.The time interval for repetition of the basic control algorithm was onesecond.

The nominal capacity factor of the wind farm for the full year was36.8%. The electrolyser modules were on 80% of the time. The powercapture for both the first and second six month periods was 99.97%,respectively. (These values are separate from the 3% losses associatedwith the power transmission and conversion path.) There was negligiblerequirement for alternative power supply for this ideal case, in whichpower measurement delays and errors are neglected.

A voltage-current relationship for the electrolyser module cells wasthen added to the computer simulation model (as opposed to assuming aconstant cell voltage of 2.0 V/cell over the operating range of currentdensities). The power captures for the first and second six monthperiods were almost unchanged, at 99.96% and 99.97%, respectively.(These values are separate from the 3% losses associated with the powertransmission and conversion path.) There was negligible requirement foralternative power supply.

Example 5

Next, the effects of power measurement delay and/or error, as well asthe effects of step type error mitigation, were modeled using data for ahalf year. The results are shown in Table 3. The largest requirement foralternative loads was 0.94% of the total wind energy, even with a largepower measuring error of 5% plus a power measuring delay of 1 second.Step type error mitigation with a +/−70 kW threshold reduced therequirement for alternative load by 31% to 0.65% of the total windenergy. The largest requirement for alternative power supply was 0.22%of the total wind energy, even with a large power measuring error of 5%plus a power measuring delay of 1 second. Step type error mitigationwith a +/−70 kW threshold reduced the requirement for alternative powersource by 18% to 0.18%. of the total wind energy

TABLE 3 Effect of Power Measurement Delay and Error on Requirement forAlternative Load and Alternative Power Source for a 51 MW Wind Farm Overa Half Year of Operation Energy to Alternative Energy to AlternativeLoad (% of Total Power Source (% of Total Case Wind Energy) Wind Energy)No Power Measuring 0.039 0 Delay or Error Delay of 1 s 0.175 0.14 Delayof 1 s + Error of 0.23 0.17 1% Error of 5% 0.92 0.20 Error of 5% + Delayof 1 s 0.94 0.22 Step Type Error 0.64 0.17 Mitigation +/− 70 kWThreshold - 5% Error Step Type Error 0.65 0.18 Mitigation +/− 70 kWThreshold - 5% Error + Delay of 1 s

The foregoing description of the preferred embodiments and examples ofthe apparatus and process of the invention have been presented toillustrate the principles of the invention and not to limit theinvention to the particular embodiments illustrated. It is intended thatthe scope of the invention be defined by all of the embodimentsencompassed within the claims and/or their equivalents.

1. A system for distributing electric power from a wind farm generatingmedium voltage DC electricity to a plurality of electrolyser modules forproducing hydrogen comprising: a. power determination and monitoringmeans for at least one of measuring, estimating and predicting the powerof said DC electricity generated by the wind farm; b. transmission linesconnected to said wind farm for transmitting said medium voltage DCelectricity from said wind farm to the vicinity of said plurality ofelectrolyser modules; c. at least one step down converter locatedproximate to said plurality of electrolyser modules for receiving saidmedium voltage DC electricity from said transmission lines andconverting it to non-regulated low voltage DC electricity; d. at leastone DC bus connected to said at least one step down converter forreceiving and distributing said low voltage DC electricity; e. at leastone regulated DC-DC converter associated with each of said plurality ofelectrolyser modules and connected to at least one of said at least oneDC bus, for receiving said non-regulated low voltage DC electricity fromsaid at least one of said at least one DC bus and supplying regulated DCelectricity to each of said plurality of electrolyser modules; f. atleast one electrolyser module controller connected to said plurality ofelectrolyser modules for monitoring and controlling said plurality ofelectrolyser modules; g. at least one dispatch controller connected tosaid power determination and monitoring means and said at least oneelectrolyser module controller for monitoring said power determinationand monitoring means and said at least one electrolyser modulecontroller and for controlling said system for distributing electricpower; h. at least one alternative load connected to at least one ofsaid transmission lines, the low voltage side of said at least one stepdown converter, and said at least one DC bus, for demanding any of saidelectric power from said wind farm that is not demanded by saidplurality of electrolyser modules; i. at least one alternative powersource connected to at least one of the medium voltage side and the lowvoltage side of said at least one step down converter, and said at leastone DC bus, for supplying any of said electric power demanded by saidplurality of electrolyser modules and not supplied by said wind farm. 2.The system claimed in claim 1 wherein said at least one regulated DC-DCconverter associated with each of said plurality of electrolyser modulescomprises at least one chopper type converter.
 3. The system as claimedin claim 1 further comprising a power balancing controller.
 4. A methodfor distributing electric power from a wind farm for generating mediumvoltage DC electricity to a plurality of electrolyser modules forproducing hydrogen comprising the steps of: a. at least one ofmeasuring, estimating and predicting the power of said DC electricitygenerated by the wind farm; b. estimating power transmission andconversion losses; c. transmitting said medium voltage DC electricity tothe vicinity of said plurality of electrolyser modules; d. convertingsaid medium voltage DC electricity to non-regulated low voltage DCelectricity using at least one step down converter; e. distributing saidnon-regulated low voltage DC electricity via at least one DC bus; f.receiving and regulating said non-regulated low voltage DC electricityusing at least one regulated DC-DC converter associated with each ofsaid plurality of electrolyser modules and connected to at least one ofsaid at least one DC bus, and supplying regulated DC electricity to eachof said plurality of electrolyser modules according to at least one ofmeasured, estimated and predicted power of said medium voltage DCelectricity generated by said wind farm and estimated power transmissionand conversion losses; g. directing any electric power generated by saidwind farm that is not demanded by said plurality of electrolyser modulesto at least one alternative load; h. supplying any electric powerdemanded by said plurality of electrolyser modules that is not suppliedby said wind farm from at least one alternative power source.